The present invention relates to a keyboard electronic musical instrument, and in particular to a circuit for automatically generating a bass note corresponding to the lowest key depressed on one of the manuals other than the pedalboard. In a broader aspect, the invention also relates to a circuit for generating a single pulse in a serial data stream in response to the last-occurring pulse in the data stream produced by multiplexing a manual of the instrument.
Present-day electronic organs generally fall into three classes: smaller home organs which are voiced to simulate a wide range of modern instruments but are not designed to closely simulate a pipe organ, electronic theater organs which simulate the characteristic sound of a theater pipe organ, and institutional or classical organs which simulate pipe organs generally found in churches and concert halls. Although classical pipe organ literature is best played on a true pipe organ, such organs are very expensive and require frequent maintenance to maintain the pipes in tune. Furthermore, changes in humidity and temperature affect the operation and sound of the organ, and the number of technicians who can maintain and tune pipe organs is rapidly dwindling. Consequently, pipe organs have become so expensive that they are beyond the means of most musicians and many churches.
In order to permit classical literature to be played, electronic organs have been developed which simulate, to varying degrees of closeness, the sound of a pipe organ. One approach is to utilize a pure digital system wherein the sounds produced by the various instruments are digitally stored in memories which are then addressed at a variable rate depending on the keys depressed to produce the tones of the instruments at the frequencies desired. Systems of this type have unique problems which prevent them from being completely satisfactory, however. Firstly, the number of harmonics as a function of the frequency of the waveform varies somewhat because of the limited number of sample points at low frequencies, and, secondly, aliasing is a significant problem. Other organs of this type utilize pure analog techniques where individual tone generators produce the various voices and complex switching arrangements are utilized to key the various tones. The circuitry and switching arrangement for such an organ is extremely complex and unwieldy, however, and this greatly increases the physical size and cost of the organ as well as posing significant maintenance problems. The third approach, and that which is employed in the present system, is to combine digital and analog techniques to utilize the advantages inherent in each of them.
In a pipe organ or an electronic organ simulating a pipe organ, the upper manual is referred to as the Swell manual because the volume of those voices was traditionally controlled by a swell chamber having a series of shutters which opened and closed under the control of the organist. The lower manual is referred to as the Great manual, and it, like the Swell manual, comprises sixty-one keys. The pedal manual comprises thirty-two pedals arranged in a convex pattern. The voice controls are referred to as stops and take the form of rocker tabs, blade-type tabs or drawbars.
Such organs also include a particular type of special effect control known as couplers, both intermanual and intramanual. Intermanual couplers enable voices normally assigned to one manual, including the pedalboard, to be played on another manual. For example, the pedalboard can be caused to play voices assigned to certain ranks of the Great manual, or the Swell manual may be coupled to the Great manual and vice versa. Intramanual couplers, on the other hand, enable expansion of the basic rank of pipes. For example, if an eight foot flute voice is played on the Great manual, and the four foot Great to Great coupler is activated, the organ will produce both the eight foot flute and the four foot flute. Likewise, if the sixteen foot Great to Great coupler is actuated, a sixteen foot flute will also be played.
A technique which is often employed in pipe and electronic organs is referred to as unification, which permits more ranks of pipes or voices to be produced without duplicating each pipe or voice in the rank. For example, a rank of diapasons at the eight foot level requires sixty-one pipes, and in a non-unified system, to add a rank of four foot diapasons, an additional sixty-one pipes would be necessary, for a total of one hundred twenty-two pipes. However, of the five octaves of four foot diapasons, four of them are exactly at the same pitch as the original eight foot rank of diapasons, so that there are forty-eight redundant pipes. In a unified system, then, for each additional footage, only twelve pipes or keyers are added, so that for the combined two foot, four foot, eight foot and sixteen foot ranks, a total of only ninety-seven pipes or keyers are necessary. The disadvantage to this is that the chorus effect is not as pronounced, but this is offset by the very substantial cost savings.
Pipe organs are capable of producing voices known as mixtures, which comprise two to five or more pitches produced simultaneously by depressing a single key. The pitches are generally unison and mutation pitches, so that a 1 3/5 foot mixture comprises a 2 foot pitch, a 1 3/5 foot pitch, and a 1 foot pitch, for example. The rank of the mixture determines the pitches that are played, so depending where on the manual the key is depressed, the mixture will comprise either two unison and one mutation, as in the previous example, or two mutations and one unison. In this latter case, the mixture would comprise, for example, a 11/3 foot pitch, a 2 foot pitch, and a 22/3 foot pitch.
In an electronic organ of the type in question, there are, of necessity, a large number of interconnections between the manuals, keyswitches, couplers, stops, keyers and tone generators, which results in a very complex system. Such complexity greatly increases the cost of manufacturing and maintaining the organ and provides numerous opportunities for malfunctions to develop.
With organs of the classical variety having two or more manuals and a full pedalboard, they are extremely difficult instruments to play with any degree of proficiency. Not only must the organist play with both hands on one or more of the manuals, but must also coordinate his or her feet, which are used to play the pedals. In much classical literature, the staff of music which is written for the pedals is often of a high degree of difficulty, and therefore requires a proficient musician to play it properly.
A problem which is encountered in many churches in small communities, is that they are not able to attract an organist having sufficient skill to play the pedals with any degree of proficiency. Persons able to play the piano are usually quite readily available, however, and they generally are able to play the music written for the upper manuals of the organ because the keys are arranged similarly to those of a piano. This is not entirely satisfactory, however, because when the pedals of the organ are not played, the music lacks the characteristic fullness of a pipe organ.
Prior attempts to solve this problem have involved circuitry which plays one or more bass notes corresponding in note name to a key or group of keys played on the accompaniment manual but sounding one or more octaves lower. In many cases, this has been accomplished by rather complex switching arrangements, which have proven to be troublesome from the standpoint of manufacturing costs and difficulty of maintenance. To reduce the switching complexity, other solutions have entailed scanning of the accompaniment manual from the lower keys to the higher keys and producing a control pulse corresponding to the first depressed key of the accompaniment manual which is encountered. Since this is, of necessity, the lowest depressed key on the accompaniment manual, the system works reasonably well as long as the scanning is from low to high. Problems are encountered, however, where the manual is multiplexed from high to low, as it is in systems where the lower frequency footages are generated by delaying the keydown pulses in the data stream and then recombining them to form a composite data stream comprising the original keydown pulses as well as footage pulses in octavely related time slots.
It has been found that a reasonably full organ sound can be obtained by producing an additional tone corresponding in pitch to the lowest tone placed on the Great manual but voiced as if it were played by the pedalboard. Since this note on the accompaniment manual is not the first note in the data stream but the last note, problems arise because if the data stream is considered in real time during a scan of the manual, there is no information in the data stream which indicates whether the keydown pulse at any particular time is the last one in the data stream, or if a lower key has been depressed thereby producing yet another keydown pulse. Although long delay lines or utilization of dynamic registers or memories could be utilized to store the data stream for a preceding scan so that the proper keydown pulse during the next scan can be selected as that pertaining to the lowest depressed key on the accompaniment manual, such systems are quite complex and add significantly to the manufacturing cost of the organ.
The problem to be solved, then, is the provision of a circuit which will detect the last keydown pulse in the serial data stream and utilize this information to key a tone which is then voiced as if it were played by the pedals, and to accomplish this efficiently from the standpoint of circuit requirements.